This invention relates to belts used in continuously variable transmissions (xe2x80x9cCVTxe2x80x9d), and more particularly to CVT belts comprising blocks indexed on endless tensile members.
It is well known in the art that a gear type transmission may be used for running a motor vehicle, motorcycle or the like. For the purposes of improving fuel efficiency, a continuously variable transmission, CVT, is preferable. Various types of belts have been developed for use in continuously variable transmissions.
Generally, the CVT Belts have a silhouette similar to that of a conventional V-belt. In particular, they are broad at the top and narrow at the bottom and designed to fit between the sheaves of a pulley defining an angular groove. The pulley on which the belt is trained comprises a moveable sheave and a fixed sheave, both having a truncated cone shape. Generally, one of the sheaves moves while the other remains fixed.
Moving one sheave in relation to the other effectively varies the effective diameter xcfx86 of the pulley within which the belt operates. Consequently, belt speed is a function of the effective diameter of the pulley which is in turn a function of the axial position of the sheaves relative to each other.
Representative of the art is U.S. Pat. No. 4,813,920 to Inukai. The disclosed belt comprises a plurality of blocks which engage at least one endless load carrier in the lengthwise direction of the belt. The blocks are provided with means to hold each in a substantially perpendicular position on the load carrier.
It is also known in the art that in the case of a dry running CVT belt, the outer inclined surface of the block which contacts the surfaces of the pulley sheaves must be comprised of either thermal setting or thermal formed plastic. Using such plastics negates the need for lubrication between the belt and the sheave surface. Blocks may have such plastics only on the inclined surface designed to interface with the pulley sheave or be totally over molded with plastic.
Reference is made to U.S. Pat. No. 4,813,920 to Inukai which discloses an over-molded metal reinforced block type CVT Belt. The over molding is accomplished by chemical preparation of the surface of the reinforcing member. This may involve surface preparation by alkaline soaking process with an acid soaking process. An adhesive layer is then applied to the metal member block consisting of a silane coupling agent, which consists of an amino alkoxy silane. The phenol plastic is then over-molded on the prepared metal member. Of course, the chemical preparation of the metal block requires use of hazardous materials. This creates special handling requirements for the chemicals used to treat the metal blocks as well as for disposal of the chemicals once they have been used. Japanese laid open application JP11-82637-A teaches chemical preparation of a metal reinforced block body prior to application of the plastic over-molding.
Inukai ""920 further teaches locating the center of gravity of the blocks within a diameter of a tensile member. It is taught that placement of the center of gravity of the block in proximity to the centerline of the tensile member may reduce oscillation of the blocks during operation. This places requirements on the design of the blocks so the center of gravity is properly located. However, it is questionable whether such placement is advantageous.
Another aspect of the block type CVT belts in that the blocks comprise upper and lower arms connected by a central pillar. The transitions between the pillars and the arms are generally right angles. Such right angle connections create stress risers that decrease the life of the blocks due to failure of the upper arm connection to the central pillar, thereby decreasing the life of the belt.
What is needed is a block type CVT belt having a center of gravity of each block that is asymmetrically located relative to a geometric center of the block. What is needed is a block type CVT belt having a metal reinforced block. What is needed is a block type CVT belt having an over-molded metal reinforced block. What is needed is a block type CVT belt having an over-molded metal reinforced block wherein the surface preparation of the metal reinforcement is accomplished by mechanical means. What is needed is a block type CVT belt having a complex radius between a pillar and an upper and lower support arm. What is needed is a block type CVT Belt having a groove with a complex shape surface on a lower portion. The present invention meets these needs.
The primary aspect of the invention is to provide a block type CVT Belt having a center of gravity of each block that is asymmetrically located relative to a geometric center of the block.
Another aspect of the invention is to provide a block type CVT Belt having a metal reinforced block.
Another aspect of the invention is to provide a block type CVT Belt having an over-molded metal reinforced block.
Another aspect of the invention is to provide a block type CVT Belt wherein the surface preparation of the metal reinforcement is accomplished by mechanical means.
Another aspect of the invention is to provide a block type CVT Belt having a complex radius between a pillar and an upper and lower support arm.
Another aspect of the invention is to provide a block type CVT Belt having a groove with a complex shape surface on a lower portion.
Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings.
The block type CVT belt according to the present invention comprises at least one endless load carrier having tensile members. A plurality of blocks are transversely engaged with the load carrier in a lengthwise direction of the belt. The center of gravity of each block is asymmetrically located in each block. Each block has thermoset or thermoplastic over-molding. The over-molding is attached to the metal block by use of an adhesive or primer and adhesive. The preparation of the metal reinforcing member is accomplished by mechanical tumbling means, as opposed to chemical preparation. Each block also comprises at least one slot for receiving the load carrier. Each slot having an upper concave surface and a lower surface having a complex shape. The upper concave surface receives a corresponding convex surface or tooth on an upper surface of the tensile member. Each slot is provided with a complex radius between a central pillar and an upper and lower arm in order to avoid stress risers. The load carriers are slightly compressed in each groove to significantly reduce skew.